A Study of a High-Energy Gamma-ray Spectrum Produced by 9Be(α,nγ)12C Reaction to Diagnose the Escaping Helium from a Fusion PlasmaA Study of a High-Energy Gamma-ray Spectrum Produced by 9Be(α,nγ)12C Reaction to Diagnose the Escaping Helium from a Fusion PlasmaAA12528887